Generator systems that are installed in aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, electrical aircraft systems.
Among the important components in such generator systems are the rotors of the exciters. Conventional exciter rotors are formed from multiple laminations that are thin plates that are stacked axially along the generator shaft. The rotors often have many (e.g., more than eight) poles, and also support the rectifier circuits that convert the AC power generated in the rotor windings into the DC power that is to be provided to the main generator rotor.
Such conventional exciter rotors have several limitations. Because the generators installed in aircraft will often be variable frequency generators that rotate in the speed range of 12,000 rpm to 24,000 rpm, large centrifugal forces are imposed upon the rotors of the generators. Because the structure of the rotor includes multiple laminations, and because the laminations often are made from materials that are limited in their strength, imbalances in the rotor can occur when changes or shifts in the laminations affect the relative alignment of the laminations with one another or with respect to the generator shaft. Additional imbalances can occur when shifting or other changes in the positioning of the laminations affect the positioning of the many wire windings or rectifier circuits being supported by the laminations. Such imbalances can create inefficiencies in the operation of the generators or risk potential failures.
Additionally, the use of laminations in the exciter rotors makes it difficult to accurately and consistently manufacture such rotors. Slight variations in the thicknesses of the laminations of the exciter rotor can make it difficult to predictably manufacture exciter rotors having a given overall axial thickness. Further, the complicated shape of the laminations, with their many radially protruding pole extensions and deep radial cut-outs, often renders it difficult to manufacture and assemble the laminations.
Hence, there is a need for a new exciter rotor assembly that is reliable, robust and can be easily manufactured within tolerances both in terms of the shape of the outer perimeter of the rotor and the axial thickness of the rotor. Additionally, there is a need for a new exciter rotor assembly that is capable of maintaining proper balance when operating at high speeds even though it includes multiple laminations and supports many wire windings and rectifier circuits.